Heat packs utilizing supercooled aqueous salt solution have been used for the treatment of soreness of muscles of athletes and sportsmen. Heat packs are also used as infant heel warmers in medical facilities as an aid in drawing blood. Such supercooled solutions include aqueous solutions of sodium acetate and calcium nitrate tetrahydrate.
Various techniques of initiating crystallization have been proposed, including inserting a crystal of material into the supercooled solution, injecting air by means of a valve, scraping metal into the container, and squeezing a plurality of rigid objects. Examples of these techniques and others are disclosed in U.S. Pat. Nos. 1,915,523, 1,433,010, 2,289,425, 2,220,777, 3,093,308, 4,077,390, 4,572,158, 5,275,156 and 5,305,733.
The present invention provides a trigger made from a support material to which adhere dry or partially dry particles. Such a trigger is typically made from sand paper which is easily manufactured and used. The trigger is used by manipulating to cause the dry or partially dry particles to be released into the salt solution. Preferably, the trigger can be activated using one hand. None of the above references disclose the claimed invention.